Many types of cells can be cultured in vitro in suspension or as adherent cultures. Some cells, such as blood cells, naturally live in suspension, without being attached to a surface. In contrast, most cells derived from solid tissues are adherent. Some examples of adherent cells that can be cultured include epithelial cells, hematopoietic cells, mast cells, neurocytes, hepatocytes, hepatic parenchymal cells, bone marrow cells, osteoblasts, fibroblasts, and epidermal cells. Many types of adherent stem cells can also be grown in culture. Some examples of stem cells include pluripotent stem cells, induced pluripotent stem cells, embryonic stem cells, adult stem cells, and multipotent and induced multipotent stem cells.
Generally, adherent cells are grown on a surface, such as the surface of a cell culture dish or on a microcarrier. Adherent cells naturally adhere to one another and to surfaces, which in some ways mimics the in vivo lifestyle of the cells. Often the surface is coated with extracellular matrix components such a collagen and/or elastin to increase adhesion properties and provide other signals needed for growth and differentiation.
When cultured cells are ready for harvesting, chemical means such as enzymes (e.g., collagenase) and/or physical means such as glass capillary colony cutters have generally been used to separate the cells from the surface. However use of chemicals, enzymes, and/or physical means to separate cultured cells from the surface can damage the cells. Additionally, harvesting can damage the cells if the cells are not separated from the surface prior to harvesting. Further, these chemical and physical methods can be time consuming, tedious, and costly.